Free-running relay multivibrator



June 23, 1959 .1. H. SPEER, JR

FREE-RUNNING RELAY MULTIVIBRATOR Filed April 10, 1956 GND.

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Jon/v l1. .SPEER JR.

INVEN TOR ATTORNEY United States Patent Ofiice 2,892,105 FREE-RUNNINGRELAY MULTIVIBRATOR John Howard Speer, Jr., Santa Monica, Calif.,assignor to Hughes Aircraft Company, Culver City, Calif., a corporationof Delaware Application April 10, 1956, Serial No. 577,400 Claims. (Cl.307-132) The present invention relates to multivibrators in general andmore specifically to a free-running relay multivibrator that producespulse-type oscillations controllable as to frequency, phase, and as tothe on-oft times of the pulses.

Standard free-running vacuum tube multivibrators and relay oscillatorsare customarily used to provide pulsetype oscillations. at two sets ofoutput terminals. In the case of vacuum tube multivibrators, thefrequency as Well as the on-01f times of the pulses may be varied. Inthe case of relay oscillators, on the other hand, the frequency of thepulses can be varied. In neither case can the phase between theoscillations be adjusted. More specifically, in the prior artmultivibrator and oscillator devices, the phase is fixed, the pulsesproduced at one set of output terminals being 180 out of phase with thepulses produced at the other set of output terminals. Phase adjustmentmay be important where the pulses are employed to drive incrementaldevices, such as solenoid driven switches and incremental motors.

It is, therefore, an object of the present invention to provide afree-running relay multivibrator that produces pulse type oscillationscontrollable as to phase as well as to the frequency and on-ofi times ofthe pulses.

The present invention overcomes the phase limitations of the prior artmultivibrator and relay oscillator devices by providing a relaymultivibrator whose output pulse-type oscillations may be controlled asto phase by adjustment of the circuit parameters. More particularly, apair of relays are interconnected by impedance means having exponentialvoltage rise and decay characteristics. Upon applying a direct-currentvoltage to the relay multivibrator, a voltage alternately rising anddecaying exponentially is developed across the solenoid of each relay.By varying the appropriate parameters of the impedance means, that is,by varying either the rise or decay characteristics of the impedancemeans, or both, the phase or" the oscillations as well as the frequencyand on-oii times of the pulses may be varied as desired.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages thereof, will be better understoodfrom the following description considered in connection with theaccompanying drawings in which an embodiment of the invention isillustrated by way of example. It is to be expressly understood,however, that the drawings are for the purpose of illustration anddescription only, and are not intended as a definition of the limits ofthe invention.

Fig. l is a schematic circuit of a free-running relay multivibratoraccording to the present invention;

Fig. 2 is a composite diagram of waveforms repre sentative of thevoltages. produced at various points in the circuit of Fig. l and Fig. 3is a composite diagram of waveforms illustrating the closing and openingof the relay contacts of the relays shown in Fig. 1.

Referring now to the drawings, there is shown in Fig. 1

2,892,105 Patented June 23, 1959 a preferred embodiment of afree-running relay multivibrator, according to the present invention,that pro duces pulse-type oscillations at a first pair of outputterminals 10 and at a second pair of output terminals 11, the relativephase of the oscillations as well as the frequency and on-off time ofthe pulses being adjustable by adjustment of the circuit parameters.

As shown in the figure, the relay multivibrator basically comprises apair of relays, generally designated 12 and 13 shown here as being ofelectromagnetic type. More specifically, relay 12 includes a core 14having a coil 15 wound thereon, a pair of relay contacts 16 and 17, anda relay arm 18 positioned between relay contacts 16 and 17. The relayarm is shown as being in physical and electrical contact with relaycontact 16 in one relay position and magnetically coupled to core 14 asindicated by dashed line 20. In the other relay position, the relay arm18 will, of course, be in electrical contact with the second relaycontact 17. Similarly, relay 13 includes a core 21 having a coil 22wound thereon, a pair of relay contacts 23 and 24, and a relay arm 25positioned between relay contact 23 and 24. The relay arm is shown asbeing physically and electrically in contact with relay contact 23 in afirst position and magnetically coupled to core 21 as indicated bydashed line 26. In the second position, the relay arm 25 will be inelectrical contact with relay contact 24. Obviously, other types ofrelay construction may also be utilized.

The relay multivibrator further includes a pair of capacitors 2'7 and28, capacitor 27 being electrically connected in parallel with coil 15and capacitor 28 being electrically connected in parallel with coil 22.A variable resistor 30 is preferably connected in parallel withcapacitor 27 and a variable resistor 31 is preferably connected inparallel with capacitor 28. Thus, coil 15, capacitor 27 and variableresistor 30' form a parallel combination, one junction of thecombination being connected to ground and the other junction of thecombination, designated 32, being electrically connected through avariable resistor 33 to relay contact 24. Similarly, coil 22, capacitor28 and variable resistor 31 form a parallel combination, one junction ofthe combination being connected to ground and the other junction of thecombination, designated 34, being electrically connected through avariable resistor 35 to relay contact 16.

One terminal of terminals 10 is connected to ground, the other of saidterminals being electrically connected to relay contact 17. Similarly,one terminal of terminals 11 is grounded, the other of said terminalsbeing electrically connected to relay contact 23. Relay arm 18 iselectrically connected to relay arm 25 by means of lead 36 which iselectrically connected to a source of direct-current voltage indicatedas B+.

Considering now the operation, direct-current voltage from the voltagesource B+ is applied to the relay multivibrator at a time t as shown inFig. 2. Accordingly, at time t electrical current commences to flow fromthe voltage source B+ through relay arm 18, relay contact 16, variableresistor 35 and the parallel combination of coil 22, capacitor 28 andresistor 31 to ground. As a result, capacitor 28 positively charges atan exponential rate and, in consequence thereof, the potentialat'junction point 34 or, stated differently, the voltage acrosscapacitor 28 increases exponentially toward a voltage level V as shownby waveform 36 in Fig. 2, V being equal to B+ voltage multiplied bywhere R6011 being the resistance of coil 22, and R l-R being theresistance of resistors 31 and 35, respectively. The voltage acrosscapacitor 28, that is, voltage 36 reaches the pull-in value of voltageof relay 13 at time Consequently, at time t relay arm 25 is magneticallyattracted by core 21 so that the arm moves quickly out of electricalcontact with relay contact 23 and into electrical contact with relaycontact 24, as indicated by waveform 37 of Fig. 3.

It should be noted that from time t to time 1 zero voltage is producedat output terminals 10, as shown by waveform 38 of Fig. 2, whereas B+voltage is produced at output terminals 11, as shown by waveform 40 ofFig. 2. This will be obvious from the fact that during time interval t1,, terminals are electrically disconnected from the B+ voltage sourcewhile, during the same time interval, terminals 11 are electricallyconnected to the voltage source.

Upon pull-in of relay 13 at time 1 the circuit of relay 12 iselectrically connected through resistor 33 to voltage source B+. As aresult, the potential at junction point 32 or, stated difierently, thevoltage across capacitor 27 commences to rise exponentially toward avoltage level V; for the reasons previously explained in connection withcapacitor 28. The exponential rise of voltage across capacitor 27 isshown as wave form 41 in Fig. 2.

The voltage developed across capacitor 27, that is, voltage 41 reachesthe pull-in value of voltage of relay 12 at time t Consequently, at timerelay arm 18 is magnetically attracted by core 14 so that the arm movesquickly out of electrical contact with relay contact 16 and intoelectrical contact with relay contact 17, as indicated by waveform 42 inFig. 3. Thus, at time 1 output tor-- minals '10 are electricallyconnected to the voltage source and voltage 38 produced at these outputterminals immediately rises to a 13+ voltage level.

Upon pull-in of relay 12, the circuit of relay 13 is electricallydisconnected from the 13+ voltage source. As a result, capacitor 28discharges exponentially through coil 22 and resistor 31 so that voltage36 developed across capacitor 28 decreases exponentially toward zerovoltage. Voltage 36 reaches the drop-out value of voltage of relay 13 attime t At this point in time, relay arm is released by core 21 and, as aresult, the arm quickly moves out of electrical contact with relaycontact 24 and into electrical contact with relay contact 23, as shownby waveform 37 of Fig. 3. Thus, at time t output terminals 11 are againelectrically connected to voltage source B+ and voltage 40 produced atthese output terminals is again at a 13+ voltage level.

Furthermore, the drop-out of relay 13 electrically disconnects or breaksthe circuit between relay 12 and voltage source B+ so that capacitor 27commences to discharge exponentially through coil 15 and resistor 30.

Accordingly, voltage 41 developed across capacitor 27 commences todecrease exponentially toward zero voltage. Voltage 41 reaches thedropout value of voltage of relay 12 at time 12,, and, when this occurs,relay arm 18 quickly moves out of electrical contact with relay contact17 and into electrical contact with relay contact 16, as shown bywaveform 42 of Fig. 3. Consequently, at time 1 output terminals 10 areagain electrically disconnected from the voltage source and voltage 38produced at output terminals 10 immediately drops from B+ to zero. Atthe same time, the electrical circuit of relay 13 is again connected tovoltage source 13+ and voltage 36 developed across capacitor 28 againincreases exponentially toward voltage V Thus, relays 12 and 13 arealternately connected and disconnected to and from voltagesource 8+ and,in consequence thereof, voltages 38 and 40 produced at output terminals10 and 11, respectively, are that of a pulse-type oscillation, asillustrated by waveforms 38 and 40 of Fig. 2.

It should be noted that the pull-in and drop-out rates of both relaysare determined by the circuit parameters,

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namely, variable resistors 30, 31, 33 and 35 and capacitors 27 and 28,and, therefore, that the relative phase of the oscillations produced atoutput terminals 10 and 11, as well as the frequency and on-oft times ofthe pulses, are fixed for any one set of values of these parameters.However, the frequency phase and on-off time may be fixed at any otherdesired values by suitable adjustment of the circuit parameters. In thisregard, it will be obvious to those skilled in the art that adjustmentof resistors 30 and 31 will have a greater effect on frequency andon-oil time than resistors 33 and 35 and, conversely, adjustment ofresistors 33 and 35 will have a greater efiect on relative phase thanresistors 30 and 31.

It should further be noted that the relay multivibrator of the presentinvention may be modified in various ways without departing from thespirit and scope of the invention. Thus, for example, to produce thesame operation and results previously described, variable inductors maybe substituted for variable resistors 33 and 35, capacitors 27 and 28taken out of the circuit, and inductors inserted in the circuit inseries with each of the relay coils 15 and 22. More explicitly, a firstinductor may be connected in series between junction point 32 and theupper end of coil 15, and a second inductor may be connected in seriesbetween junction point 34 and the upper end of coil 22.

What is claimed as new is:

l. A free-running relay multivibrator that produces pulse-typeoscillations in response to an electrical connection thereto of adirect-current source of voltage, said multivibrator comprising: firstand second electromagnetic relays, each relay having first and secondrelay contacts and a relay arm electrically connected to the directcurrent voltage source and normally in electrical contact with the firstrelay contact; and first and second impedance means each electricallyinterconnecting the coil of one relay to a contact of the other relay,each impedance means having variable exponential voltage rise and decaycharacteristics, said first impedance means being electrically connectedacross the coil of said first relay and to the second relay contact ofsaid second relay and said second impedance means being electricallyconnected across the coil of said second relay and to the first relaycontact of said first relay, whereby a voltage alternately rising anddecaying exponentially is developed across the coil of each relay.

2. The relay multivibrator defined in claim 1 wherein said first andsecond impedance means include first and second capacitors electricallyconnected across the coils of said first and second relays,respectively, said first and second impedance means further includingfirst and second resistors, respectively, said first resistor beingelectrically connected between said first capacitor and the second relaycontact of said second relay and said second resistor being electricallyconnected between said second capacitor and the first relay contact ofsaid first relay.

3. A free-running relay multivibrator for producing pulse-typeoscillations at first and second pairs of output terminals in responseto the connection thereto of a direct-current source of voltage, thefrequency and relative phase of the oscillations being adjustable, saidmultivibrator comprising: first and second electromagnetic relays, eachrelay including first and second relay contacts and a relay arm normallyindividually connected to the first relay contacts when said relays arenot energized, the second and first relay contacts of said first andsecond relays being electrically connected to the first and second pairsof output terminals, respectively, each relay arm. being electricallyconnected to the source of direct-current voltage; first and secondcapacitors electrically connected in parallel with the coils of saidfirst and second relays, respectively; first and second variableresistors electrically connected in parallel with said first and secondcapacitors, respectively; and third and fourth variable resistors, saidthird resistor being electrically connected between said first capacitorand the second relay contact of said second relay and said fourthresistor being electrically connected between said second capacitor andthe first relay contact of said first relay.

4. A free-running relay multivibrator that produces pulse-typeoscillations in response to the electrical connection thereto of adirect-current source of voltage, said multivibrator comprising: firstand second e1ectromagnetic relays, each relay having first and secondrelay contacts and a relay arm electrically connected to thedirectcurrent voltage source and normally in electrical contact with thesecond relay contact; first and second variable impedance elements, saidfirst impedance element being electrically connected between the coil ofsaid first relay and the first relay contact of said second relay andsaid second impedance element being electrically connected between thecoil of said second relay and the second relay contact of said firstrelay; and first and second variable impedance means electricallyconnected across the coils of said first and second relays,respectively, said first and second impedance means coacting with saidfirst and second impedance elements, respectively, to produce a voltageacross the coil of each relay that alternately rises and decaysexponentially.

5. In a relay multivibrator circuit, a power source; first and secondrelays, each having a movable contact arm connected to said powersource, and first and second contacts arranged to be alternativelyengaged by said contact arm; first and second load terminals arranged tobe connected by said relays alternately to said power source; and meansfor controlling the waveform and phase relations of current delivered tosaid load terminals, comprising first and second controlled impedances,shunted across each of said relays, and a variable impedance connectedbetween each of said first and second controllable irnpedances and theone of the relay contacts associated with the other of said relays.

References Cited in the fileof this patent UNITED STATES PATENTS HinesMar. 12, 1946 FOREIGN PATENTS 528,132 Great Britain Oct. 27, 1940

